Pharmacology in Surgery Flashcards

A patient taking clopidogrel requires an elective total hip replacement. According to UK guidelines, how many days before surgery should clopidogrel ideally be stopped?

Answer: 7 days

Clopidogrel irreversibly inhibits the P2Y12 ADP receptor on platelets for the platelet's lifespan (7-10 days). UK guidelines (NICE, AAGBI) recommend stopping clopidogrel 7 days before elective surgery to allow sufficient new platelet production. The decision must balance bleeding risk against thrombotic risk, particularly in patients with recent coronary stents.

Which intravenous fluid most closely resembles the electrolyte composition of plasma and is recommended as first-line for fluid resuscitation in the UK?

Answer: Hartmann's solution (compound sodium lactate)

Hartmann's solution (Ringer's lactate/compound sodium lactate) contains Na+ 131, K+ 5, Ca2+ 2, Cl- 111, and lactate 29 mmol/L — closely matching plasma composition. NICE guidelines (CG174) recommend balanced crystalloids like Hartmann's as first-line for resuscitation. Normal saline has supraphysiological chloride (154 mmol/L), which can cause hyperchloraemic metabolic acidosis with large-volume use.

Metformin should be withheld before surgery primarily because of the risk of which life-threatening complication?

Answer: Lactic acidosis

Metformin inhibits hepatic gluconeogenesis and mitochondrial complex I. In the perioperative period, reduced renal perfusion (from fasting, haemorrhage, or hypotension) impairs metformin clearance, leading to accumulation. This can precipitate type B lactic acidosis (mortality up to 50%). UK guidelines recommend omitting metformin on the day of surgery and restarting when eating and drinking normally with adequate renal function.

Which antiemetic acts primarily as a serotonin 5-HT3 receptor antagonist and is commonly used for post-operative nausea and vomiting?

Answer: Ondansetron

Ondansetron is a selective 5-HT3 receptor antagonist that blocks serotonin at the chemoreceptor trigger zone and vagal afferents. It is widely used for PONV and chemotherapy-induced nausea. It has few sedative effects but can cause QT prolongation and constipation. Metoclopramide is a D2 antagonist, cyclizine is an H1 antagonist, and haloperidol is a D2 antagonist.

A patient develops an anaphylactic reaction during induction of anaesthesia. What is the first-line drug treatment and route of administration?

Answer: Intramuscular adrenaline 500 micrograms (0.5 mg)

According to Resuscitation Council UK guidelines, intramuscular adrenaline (500 micrograms = 0.5 ml of 1:1000 in adults) is the first-line treatment for anaphylaxis. Adrenaline reverses bronchospasm (beta-2), supports blood pressure (alpha-1), and reduces mediator release from mast cells (beta-2). The IM route is preferred in most settings as IV adrenaline carries a risk of arrhythmia and requires careful titration.

Which proton pump inhibitor is preferred for use via the intravenous route in the acute management of upper gastrointestinal bleeding?

Answer: Omeprazole or pantoprazole

IV proton pump inhibitors (omeprazole 80 mg bolus then 8 mg/hour, or pantoprazole equivalently) are used in acute upper GI bleeding to raise gastric pH above 6, stabilising clots and reducing rebleeding rates. NICE guidelines recommend high-dose IV PPI after endoscopic haemostasis for high-risk ulcers. Ranitidine (H2 blocker) is less effective at achieving the required pH elevation.